1. Field of the Invention
The present invention relates to a vibration controller and a vibration control method for active vibration insulators, vibration controller and method which can actively inhibit vehicles from vibrating.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 8-44, 377 and Japanese Unexamined Patent Publication (KOKAI) No. 2001-140, 974, an adaptive control method, for example, an adaptive control method which uses an adaptive minimum mean squared filter, (hereinafter referred to as “Filtered-X LMS” filter) or a retarded harmonic synthesizer minimum mean squared filter (hereinafter referred to as “DXHS LMS” filter), has been applied to controlling the vibrations of an engine mount equipped with an actuator, an automotive active vibration insulator. In an adaptive control method, the filter coefficient of a “Filtered-X LMS” filter is updated sequentially to compensate the amplitude and phase of control signals for actuating an engine mount. Accordingly, outputs from a controlled system inhibit external forces resulting from the vibrations of a vehicle. Consequently, it is possible to carry out an adequate control depending on the types of vibration.
Moreover, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 11-259, 147, a simplified method referred to as a map control method has been carried out. In the map control method, an optimum filter coefficient is determined for every arbitrary engine revolution in advance using an adaptive control method. The resulting optimum filter coefficient data are stored as a data map. The stored data map is retrieved as a ROM, for example, to carry out an active control adaptable to vehicle control devices. The map control method is good in terms of the control response, because it can simply select data from the data map to generate a control signal depending on the frequency of cyclically pulsating signals.
However, in a vibration control method for active vibration insulators using an adaptive control method, the control response has been retarded because the filter coefficient is updated sequentially. Accordingly, in a range of vibration whose frequency is as low as 50 Hz approximately, such as automobiles under idling, there arises a problem that the vibration control might impair the ride quality, because passengers might perceive the vibration intensely. Moreover, when an engine is installed to a vehicle sub frame, a vibration of the sub frame and a vibration of the engine might resonate in a range of vibration whose frequency is higher than 50 Hz, especially, in a range of vibration whose frequency is 80 Hz or more, such as automobiles under running. When such a resonant vibration is added to the inherent vibration of vehicle, the phase of control signal might possibly become unstable because the control response has been retarded in an adaptive control method. In this instance, there might arise a fear that the control signal oscillates to result in loss of control.
On the other hand, in the map control method, the number of data maps are limited. Accordingly, there arises a problem that it is difficult to cope with controls which require a large number of data maps depending on control conditions. For example, in a range of vibration whose frequency is high, such as automobiles under running, various driving operations affect vibrations which passengers perceive. Consequently, it is difficult for the map control method to fully cope with various vibrations. Thus, there is a problem that the map control method might impair the ride quality.